1. Field of the Invention
The present invention relates to an electret condenser microphone available for various audio equipments such as a cellular phone, and more particularly to an electret condenser microphone equipped with a capacitor unit constituted by an electrode plate and a diaphragm to receive an acoustic wave to be converted to an acoustic signal indicative of the acoustic wave.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of conventional electret condenser microphones each equipped with a capacitor unit constituted by an electrode plate and a diaphragm to receive an acoustic wave to be converted to an acoustic signal indicative of the acoustic wave.
The conventional electret condenser microphones of this type have so far been available for various audio equipments such as a cellular phone. One typical example of the conventional electret condenser microphones is exemplified and shown in FIGS. 8 and 9. The conventional electret condenser microphone 900 thus proposed comprises a casing member 910 in the form of a cylindrical shape, a circuit board 920 in the form of a circular shape and disposed in the casing member 910, and an electrically insulating member 930 in the form of an annular ring shape and provided on the circuit board 920.
The casing member 910 has an inlet portion 911, a side portion 912 integrally formed with the inlet portion 911 of the casing member 910, and an end portion 913 integrally formed with the side portion 912 of the casing member 910. The circuit board 920 has a peripheral portion 921 supported by the end portion 913 of the casing member 910, and a central portion 922 integrally formed with the peripheral portion 921 of the circuit board 920 and radially inwardly extending from the peripheral portion 921 of the circuit board 920. The circuit board 920 has thereon a printed wiring. The electrically insulating member 930 is formed with a plurality of guide holes 934.
The conventional electret condenser microphone 900 further comprises an electrode plate 940 in the form of a circular shape and mounted on the electrically insulating member 930, and a plurality of electrically connecting members 950 each intervening between the circuit board 920 and the electrode plate 940 to have the circuit board 920 and the electrode plate 940 electrically connected with each other. The electrode plate 940 has thereon an electret film.
Each of the electrically connecting members 950 is in the form of a column shape and embedded in the electrically insulating member 930 under the state that each of the electrically connecting members 950 is received in each of the guide holes 934 of the electrically insulating member 930. Each of the electrically connecting members 950 has a first surface 950a held in contact with the electrode plate 940, and a second surface 950b held in contact with the printed circuit board 120.
The conventional electret condenser microphone 900 further comprises a diaphragm supporting member 960 in the form of an annular ring shape and provided on the inlet portion 911 of the casing member 910, and a diaphragm 970 in the form of a circular shape and disposed along the electrode plate 940 to be spaced apart from the electrode plate 940 at a predetermined space distance.
The diaphragm 970 has a peripheral portion 971 supported by the diaphragm supporting member 960, and a central portion 972 integrally formed with the peripheral portion 971 of the diaphragm 970 and radially inwardly extending from the peripheral portion 971 of the diaphragm 970 to be oscillatable with respect to the casing member 910.
The conventional electret condenser microphone 900 further comprises an electrically insulating spacer 980 in the form of an annular ring shape and intervening between the electrode plate 940 and the diaphragm 970 to have the electrode plate 940 and the diaphragm 970 spaced apart from each other at a predetermined space distance.
The electrode plate 940 and The diaphragm 970 collectively constitutes a capacitor unit 902 to generate an electrical capacitance corresponding to the space distance between the electrode plate 940 and the diaphragm 970 under the state that the acoustic wave is transmitted to the diaphragm 970 to have the central portion 972 of the diaphragm 970 oscillated with respect to the casing member 910.
The conventional electret condenser microphone 900 further comprises a covering member 982 in the form of a circular shape and provided on the inlet portion 911 of the casing member 910. The inlet portion 911 of the casing member 910 is formed with an acoustic aperture 918 to have the acoustic wave transmitted to the diaphragm 970 through the covering member 982 and the acoustic aperture 918 of the inlet portion 911 of the casing member 910.
The conventional electret condenser microphone 900 further comprises a signal converting unit 990 designed to convert the electrical capacitance generated by the capacitor unit 902 to the acoustic signal indicative of the acoustic wave transmitted to the diaphragm 970.
The signal converting unit 990 is provided on the circuit board 920 and surrounded by the electrically insulating member 930. The signal converting unit 990 includes a field effect transistor 991. The signal converting unit 990 is electrically connected to the electrode plate 940 through the printed wiring of the circuit board 920 and each of the electrically connecting members 950. The signal converting unit 990 is electrically connected to the diaphragm 970 through the printed wiring of the circuit board 920, the casing member 910 and the diaphragm supporting member 960.
The conventional electret condenser microphone, however, encounters such a problem that the conventional electret condenser microphone is complicated in assmebly and thus expensive in production cost, resulting from the fact that each of the electrically connecting members is embedded in the electrically insulating member under the state that each of the electrically connecting members is received in each of the guide holes of the electrically insulating member.